Patients who suffer what is commonly called a heart attack most often experience an episode of ischemia or myocardial infarction. Myocardial infarction is a necrosis of cardiac tissue brought on by a reduction in blood flow to the infarcted area caused by either a chronic obstruction in an artery or an acute obstruction such as a thrombus in the artery.
To monitor patients for myocardial infarction, physicians may rely upon periodic EKGs (electrocardiograms) which generally require as many as ten leads to be attached to the patient. In addition, after the EKG, physicians then generally require the patient to take a stress test wherein the patient is caused to run on a treadmill until the patient is essentially exhausted to stress the heart. During and after the treadmill exercise the twelve lead EKG is used to determine if the heart continues to receive adequate blood supply while under the stress conditions. Obviously such monitoring is inconvenient to the patient. Physicians may also rely upon Holtor monitoring recordings which may last from 24 to 48 hours. These additional monitoring techniques are equally as inconvenient and in addition, are also annoying. Since all of these monitoring techniques can, at best, only be administered periodically as a practical matter, and because restenosis and thus future episodes of myocardial infarction are unpredictable events, all too often, a myocardial infarction or restenosis problem may not be detected until the patient experiences pain or suffers an episode of myocardial infarction. Unfortunately, research has shown that pain is not a reliable indicator of ischemia.
Patients who have a myocardial infarction are generally treated with drugs and angioplasty to open the artery. Each of the above-mentioned therapeutic techniques is effective in reestablishing blood flow through the effected artery. However, for each therapy, there is a percentage of patients that experience restenosis (reclosure of the artery) after therapy. Restenosis is largely an unpredictable event and the time required for the reclosure to occur may range from a matter of hours to years.
From the foregoing, it can be seen that for some patients, it is very desirable to monitor for ischemia or the presence of a myocardial infarction. Many of these patients will already have an implanted cardiac stimulation device such as a pacemaker or a combined pacemaker and defibrillator.
Implantable cardiac devices have been proposed in the art for detecting for and monitoring ischemia. Many of these devices may be solely for monitoring or incorporated into pacemakers and defibrillators. With modern day storage technology and telemetry, these devices are capable of collecting and communicating large amounts of ischemia data. Dealing with this prolific data in a meaningful way remains a challenge. The present invention addresses these issues.